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Old 1st July 2009, 04:49 PM   #1
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Default Nakamichi 410 Pre + 420 Amp

come some time ago to my shop for repair ....

in the preamplifier area i neee to replace all elctrolytics ....GIVE OR TAKE 45 OF THEM !!!!!!

it seems that japs were dealing with the wrong capacitor company at the time Normaly when i repair on these devices i select one cap to test ...and if it shows problems i replace all of them any way ....

for the particular unit i thought checking them all for fun ...ALL of them were gone ....but all

now the particular unit has a coaxial volume balance pot ..... i wonder if possible to dissasembly for cleaning and put together again ...

will see

any input regarding the particular devices is very welcome

regards sakis
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Old 3rd July 2009, 10:44 AM   #2
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Default after i had

to replace almost 50 electros that were totaly gone , i lay my hands on the amplifier section .... big syrprize !!!!!! only 4 electros in the amplifier board

2 decoupling , i feedback, 1 input ....and all the rest ceramics ....

i realy thought that this is sypposed to be high quality gear ....i realy expected higher quality parts inside ....am i missing something ????

i t realy feels strange
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Old 3rd July 2009, 01:44 PM   #3
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Default finished .....

after replaced all caps from inside .... then put the all thing together ....listen to it ...58w+58 watt more than ok but performance is average ...very average for a thing like that ...

then again i wonder if this isa cheap line from the japanese legend .... dont know
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Old 3rd July 2009, 05:05 PM   #4
hafp is offline hafp  United States
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sakis,
The nakamichi 420 amp is a low power with bi-polar output; that's what I remember...but you probably know better having been in the unit for repairs.
Guys used to use that amp to power their Quad 57's.
I got to hear that set up a while back and did not think much of it.
The 420 amp did not do much to bring out the soundstage the Quad 57's are capable of.
But maybe with your mods, it will be a much better amp once you are done with it.
Good luck.
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Old 3rd July 2009, 05:16 PM   #5
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Default thanks for the info

i was actually very dissapointed by the device ...

later on the costumer informed me that at the time and from all the range of products this was the cheapest available ...

figers .... allready whta ive done is much ....i see no pint on going further since even if i do miracles with the amp ..the pre that goes behind it is nothing really special...

so it has life for another 25 yeras and average quality .....
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Old 4th July 2009, 04:09 PM   #6
hafp is offline hafp  United States
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sakis,
Exlcellent point there.
The 410 preamp was no show stopper either...
In fact, we thought the NAD1020B sounded much better, and was so much cheaper back in the day.
Cheers
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Old 20th September 2012, 07:48 PM   #7
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some more info ...since more units keep coming in

as about the pre now beyond capacitor replacements seems that local decoupling and bypass actually helps the unit a lot

as about the main amp eventhough outputs are totally obsolete still some can be found in some authorized Kenwood shops Kenwood had a lot of models that was working with the same type of transistors so may one get lucky there but expect them to be pricy

For the main unit there is a reputation that blows outputs quite often and without obvious reason
Keep in mind that Nak people at the time had a very weird insulation system ( hard to describe also ) that can be effected even by moisture and create leak to ground or form P or N to ground .

Nak people designed a heatsink that actually has absolutely no insulators and the paint on the heatsink was expected to do the insulation job ..Bit risky i think

I had to apply capton stripes both sides to ensure 100% results ..at least in the feature amplifier will not fail from that .

Noticed:
--Increased local decoupling from 4.7 mfd to 100
--Added a better input capacitor
--Found the input filter cap a bit beefy at 680 pf and setled to 390 pf but styroflex better than ceramic

Kind regards
sakis
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Old 20th September 2012, 09:24 PM   #8
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ooops

one thing i ve missed ....

the ground scheme is also weird from today's standards its ground all around rather than a conventional star ground .
Ground is essential for the boards to work .

It is expected that since 0 from power supply is all around the case heatsinks will take ground from there and then give it to boards ...

Well it seems that this is not happening always i added wires from the real o power supply to each board .

Kind regards
sakis
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